System for Sequentially Measuring the Output of a Plurality of Light Sensors Which Generate Current in Response to Incident Light

Abstract

A system for sequentially measuring the current generated by a plurality of individual current sources such as photodiodes monitoring the light output of individual LEDs representing discrete colors arranged in an array of pixels constituting an area illumination source such as an electronic billboard includes (1) a current measuring circuit connected to each current source/photodiode; (2) a separate switch such as a switching diode connected in series with each current source/photodiode and (3) sequential control means for sequentially enabling each switch/switching diode to conduct current from the current source/photodiode to the current measuring circuit while maintaining all of the remaining switches in the disable state.

1 . A system for sequentially measuring the current generated by a plurality of light sensors, with each sensor arranged to generate a current in accordance with the incident light received by the sensor comprising:
 a) a current measuring circuit having an input connected to each of the sensors for receiving the current generated by the sensors and an output for providing an output signal in accordance with the input current;   b) a separate switch connected in series relationship with each sensor and the input to the current measuring circuit with each switch having an on condition for passing current therethrough and an off condition for blocking current therethrough; and   c) sequential control means for sequentially turning each of the switches to the on condition while maintaining the remaining switches in the off condition, whereby the current measuring circuit will measure only the current generated in the light sensor connected in series with the switch in the on condition.   
   
   
       2 . The system of  claim 1  wherein each of the light sensors comprises a photodiode and wherein each of the switches comprises a diode. 
   
   
       3 . The system of  claim 2  wherein the current measuring circuit comprises a current to voltage converter including an operational amplifier. 
   
   
       4 . The system of  claim 3  wherein the sequential control means is arranged to control the bias voltages to the switching diodes. 
   
   
       5 . A system for measuring the light output of individual LEDs representing a discrete color in a pixel in which an array of such pixels form an area illumination source and a photodiode is arranged to receive a portion of the light output from each LED(s) within each pixel representing a discrete color and produce an output current representative of the emitted light comprising:
 a) a current measuring circuit connected to each photodiode for receiving the output current therefrom;   b) a switching diode connected in series relationship with each photodiode and the current measuring circuit; and   c) sequential control means for sequentially turning on each switching diode to conduct the current from a respective photodiode to the current measuring circuit while maintaining all of the other switching diodes off so that the current measuring circuit will measure only the current generated in the photo diode connected in series with the conducting diode.   
   
   
       6 . The system of  claim 5  wherein the switching diodes are connected between the photo diodes and the current measuring circuit. 
   
   
       7 . The system of  claim 6  wherein the current measuring circuit comprises an OPAMP with its input connected to each of the switching diodes and wherein the sequential control means applies one bias voltage to render one of the switching diodes conducting and another bias voltage to maintain the remaining switching diodes nonconducting. 
   
   
       8 . A system for sequentially measuring the current from a plurality of individual current sources comprising:
 a) a current measuring circuit having an input connected to each of the current sources for receiving the current produced by the sources and an output for providing an output signal in accordance with the input current;   b) a separate switch connected in series with each current source and the measuring circuit input, each switch having an on condition for passing current therethrough and an off condition for blocking the passage of current therethrough, and   c) sequential control means for sequentially turning each switch on while maintaining the remaining switches in the off condition whereby the current measuring circuit will measure only the current from the current source connected in series with the on condition switch.   
   
   
       9 . The system of  claim 8  wherein the switch is a diode. 
   
   
       10 . A photodiode and switching diode formed as an integrated circuit with the photodiode and switching diode sharing a common substrate.